The present invention is directed to bicycles and, more particularly, to a multistage sprocket assembly for a bicycle, wherein the multistage sprocket assembly comprises at least one larger diameter sprocket and at least one smaller diameter sprocket that are mounted on a rear hub of the bicycle so as to shift a driving chain for changing the bicycle speed.
U.S. Pat. No. 4,889,521 discloses a multistage sprocket assembly that includes at least one larger diameter sprocket and at least one smaller diameter sprocket assembled in a relationship such that the center point between a pair of adjacent teeth at the larger diameter sprocket and the center point between a pair of adjacent teeth at the smaller diameter sprocket are positioned on a tangent extending along the chain path when the chain is being shifted from the smaller diameter sprocket to the larger diameter sprocket. The distance between the center points is substantially equal to an integer multiple of the chain pitch. A chain guide portion is provided at the inside surface of the larger diameter sprocket at a position corresponding to the path of the chain when the chain travels between the center points for allowing the chain to move axially of the sprocket assembly slightly toward the larger diameter sprocket. This facilitates shifting the chain from the smaller diameter sprocket to the larger diameter sprocket. One or more teeth on the larger diameter sprocket may be offset or inclined from a centerline of the sprocket body to further facilitate shifting the chain from the smaller diameter sprocket to the larger diameter sprocket.